1. Field of the Invention
The present invention relates to a gasket which is interposed together with a separate plate between valve bodies when a plurality of valve bodies are intercommunicated, each valve body having a hydraulic circuit which change the supply and discharge of operating fluid (generally, hydraulic oil) to and from frictional engaging elements of an automatic transmission.
2. Description of the Prior Art
So far as a gasket which is used in order to intercommunicate among a plurality of valve bodies which are components of hydraulic control unit for an automatic transmission, those of the type described in, for instance, "NISSAN FULL-RANGE DENSI SEIGYO AUTOMATIC TRANSMISSION SEIBIYOURYOUSHO (Nissan full-range electronic control automatic transmission maintenance and repair manual) RE4RO3A type, published by Nissan Motor Company Limited, March 1988, II-pp.58-63" have been well known by those skilled in the art.
More specifically, II-63 page of the above mentioned manual discloses a gasket to which is attached a separate one-way valve. More particularly, in order to change the supply and discharge hydraulic oil to and from the frictional engaging elements of the automatic transmission, upper and lower valve bodies are each provided with a hydraulic circuit. A separate plate which is sandwiched between upper and lower separate gaskets is interposed between the upper and lower valve bodies and each of the upper and lower gaskets and the separate plate is formed with an oil passage which in turn intercommunions between the hydraulic circuits of the upper and lower valve bodies. In addition, the separate plate on the side of the upper separate gasket is set up one-way valve which closes or opens the oil passage, and the one-way valve is pushed against the oil passage by the force of a spring. Furthermore, the one-way valve is formed with an orifice.
When hydraulic oil is supplied from the hydraulic circuit of the upper valve body to that of the lower valve body, hydraulic oil is gradually supplied through the orifice of the one-way valve to the lower valve body. On the other hand, when hydraulic oil in the hydraulic circuit of the upper valve body is discharged, the one-way valve is opened so that the oil pressure in the hydraulic circuit of the lower valve body rapidly falls.
However, since the one-way valve which is fabricated separately from the gasket is attached to the latter, there arise following problems that the number of component parts is increased, resulting in an increase in cost; the step for attaching the one-way valve to the gasket is required, resulting in an increase in production step; there is a fear that due to the difference between specifications, the one-way valve cannot be correctly attached to the gasket, resulting in an increase in product ion control step; and since the one-way valve and the gasket are fabricated separately, the position of the attached one-way valve is deviated from its correct position due to attachment errors and aging, resulting in variations in sealability and hence performance.